How to run an Asyncio task without awaiting?

Question

I need to call a task periodically but (a)waiting times are almost more than the period.

In the following code, How can I run do_something() task without need to await for the result?

 import asyncio
 import time
 from random import randint

 period = 1  # Second


 def get_epoch_ms():
     return int(time.time() * 1000.0)


 async def do_something(name):
     print("Start  :", name, get_epoch_ms())
     try:
         # Do something which may takes more than 1 secs.
         slp = randint(1, 5)
         print("Sleep  :", name, get_epoch_ms(), slp)
         await asyncio.sleep(slp)
     except Exception as e:
         print("Error  :", e)

     print("Finish :", name, get_epoch_ms())


 async def main():
     i = 0
     while True:
         i += 1
         # Todo : this line should be change
         await do_something('T' + str(i))
         await asyncio.sleep(period)


 asyncio.get_event_loop().run_until_complete(main())

Answer 1

Your problem is using the run_until_complete(main()) which does not satisfy your concurrency purpose. So, assuming your coroutine tasks (do_something()) are bounded to 5, your code will be as follows:

import time
from random import randint

period = 1  # Second

def get_epoch_ms():
    return int(time.time() * 1000.0)

async def do_something(name):
    print("Start  :", name, get_epoch_ms())
    try:
        # Do something which may takes more than 1 secs.
        slp = randint(1, 5)
        print("Sleep  :", name, get_epoch_ms(), slp)
        await asyncio.sleep(slp)
    except Exception as e:
        print("Error  :", e)

    print("Finish :", name, get_epoch_ms())

loop = asyncio.get_event_loop()
futures = [loop.create_task(do_something('T' + str(i)))
           for i in range(5)]

loop.run_forever()

for f in futures:
    f.cancel()

Here is the concurrency workflow in its output:

Start  : T0 1558937750705
Sleep  : T0 1558937750705 5
Start  : T1 1558937750705
Sleep  : T1 1558937750705 1
Start  : T2 1558937750705
Sleep  : T2 1558937750705 4
Start  : T3 1558937750705
Sleep  : T3 1558937750705 5
Start  : T4 1558937750705
Sleep  : T4 1558937750705 5
Finish : T1 1558937751707
Finish : T2 1558937754709
Finish : T0 1558937755707
Finish : T3 1558937755708
Finish : T4 1558937755708

---

However, If your coroutine tasks are not bounded you could do it:

...
async def main(loop):
    i = 0
    while True:
        i += 1
        loop.create_task(do_something('T' + str(i)))
        await asyncio.sleep(period)

loop = asyncio.get_event_loop()
loop.run_until_complete(main(loop))